What you’ll learn
Find area of trapezoids.
Key idea
Average the two base lengths before multiplying by the perpendicular height.
Use both parallel bases and halve their sum; recovering one base requires subtracting the known base from the recovered sum.
Worked example
Enter the exact value or ordered values in the format requested below.
A trapezoid has parallel bases 2 cm and 5 cm, with perpendicular height 3 cm. Enter its exact numerical area in square centimeters.
- The parallel bases sum to 7 cm; the perpendicular height is 3 cm.
- A=(b1+b2)h/2=(2+5)×3/2=21/2 square centimeters.
Answer: 21/2
Quick Check
Evaluate a worked attempt at find area of trapezoids, identify the first invalid step, and provide the correction.
For trapezoid bases 2 and 8 cm and perpendicular height 7 cm, a student writes Step 1: A=(b1+b2)h/2. Step 2: A=(2+8)×7=70 cm². Locate the first invalid step and correct the area.